The conventional methods of separating various hydrocarbons involves technology which includes extraction, absorption, distillation, etc. techniques. However, a disadvantage of utilizing these techniques involves the use of energy which, in the present time, is relatively expensive. For example, in one aspect of petroleum refining a particular application step involves the deasphalting of a heavy crude oil which is recovered from a petroleum source such as a well. The crude oil is generally first passed to an atmospheric pipe still to produce light gases as well as a variety of distillation cuts suitable for use in the synthesis of fuels such as gasoline, etc. as well as cuts which may be useful in the petrochemical industry. The bottoms or bottom fraction from this atmospheric distillation still may then be passed to a vacuum distillation still which will recover lighter products as volatile material which can then be utilized to prepare other fuels such as diesel oil. However, as the feedstocks become heavier in nature, a significant amount of the fuel oil is not volatilized in either the atmospheric or vacuum stills.
In order to recover still useable oil fractions, the heavy bottoms from the vacuum distillation still is then subjected to the action of a solvent which comprises a relatively light hydrocarbon such as a paraffinic hydrocarbon containing from 3 to 7 carbon atoms. In order to obtain the desired fractionation of useable products, a high ratio of solvent to oil is required. For example, in the case of asphaltenes which are precipitated out of the heavy fraction, a typical process will operate with a solvent to oil weight ratio of 4:1 to 10:1 depending upon the degree of oil-asphaltene separation desired. The desired oil fraction, after separation from the precipitated asphaltenes will be recovered while, due to the expense of the solvent required for the separation, it is necessary to recover the solvent for further use. The high ratio of solvent to oil usually requires energy intensive processes due to the need for recovering the solvent by volatilization.
In view of the expense associated with the volatilization processes, it is deemed necessary to provide a relatively low-cost method for recovering the solvent by separation from the oil in order to reuse the solvent in further oil recovery steps. It has now been discovered that a method for separating relatively light hydrocarbons such as those employed as solvents from relatively heavy oil may be accomplished by passing the mixture of heavy oil and solvent through a membrane of the type hereinafter set forth in greater detail whereby an effective separation of solvent from heavy oil may be effected, thus permitting the recovery and reuse of the desirable solvent in further extraction processes.